Metal oxidizes, corrodes or rusts, causing failure of structures, devices or the like metal products. There are many types of corrosion, all of which are basically due to the tendency of a refined metal to form a more stable compound. Therefore, manufactured metals have a tendency to corrode thus losing their desired properties, and failing to satisfy their intended uses over time.
Prevention or reduction of corrosion is usually dependent on the metal and its intended use. Prior approaches to controlling metal corrosion include special surface coatings, moisture absorbers, and sacrificial anodes. Each of the aforesaid approaches suffers from certain drawbacks which are described below.
Surface Coatings:
One method of protecting metal from corroding is to try to insulate the metal from the environment that promotes corrosion. Controlled environments are expensive and impractical, thus paints and other surface coatings which are applied to the metal surfaces to be protected are common. These coatings insulate the metal surface from the ambient surroundings. Some of the paints which are applied to the metal surface contain sacrificial metal particles, such as zinc or aluminum, which are suspended or mixed into the paint, and which are intended to corrode as a sacrifice, or in place of, the metal surface being protected. The main drawback to such sacrificial surface paints is the need to frequently repaint the entire surface being protected. The paint actually corrodes on the metal surface so that before the surface can be repainted, the corroded paint residue must be chipped or scraped off of the metal surface. In applications where frequent repainting is impractical, such as with automobiles, the result will be corroded paint on an automobile, which corroded paint will eventually allow the metal to corrode. Paints which do not include anodic particles can chip, scratch or wear thereby exposing the underlying metal to corrosive ambient conditions.
Another type of coating that can protect a metal from corroding is grease or oil. In certain applications, grease and/or oil can be effective to prevent metal corrosion, but in most applications this approach will prove to be messy, and short lived, and thus impractical.
Moisture Absorption:
Moisture absorbent materials are common for use in corrosion prevention. The simple act of wiping off a wet or damp metal structure, such as a knife blade, is an example of moisture absorption used to prevent metal corrosion. Another example of moisture absorption to prevent corrosion is found in packaging, wherein silicone particles and blankets are used to absorb moisture inside of the package. Silicone sprays are also commonly used for the same purpose. The general drawback with all moisture absorbers is that they all have a saturation point, and are not well suited for general applications. Obviously, rain would rapidly destroy the efficacy of this approach in an ambient environment.
Sacrificial Anodes:
Sacrificial anodes are the negative side of a cathode/anode circuit. The cathode is the positive side, and the anode is a solid piece of metal which freely gives up electrons due to its atomic composition. Three metals commonly used as the anode electron donor are zinc, aluminum, and magnesium. Typically, the metal anode will be connected to the metal to be protected by a ground strap, or by forming threads on one end of the metal anode body and screwing the anode into a tapped port in the metal being protected. A drawback with present day anodes is the fact that they tend to degrade unevenly, and often end up being adhered to the part they are protecting by anodic corrosion. Since the anodes must be periodically replaced, this adherance is undesirable. Still another problem with present day sacrificial anodes is the fact that frequently the poor consumption patterns and uneven degradation will result in pieces of the anode breaking away, which can result in problems in a circulating fluid system.
It would be very desirable to provide a sacrificial anode device that would operate with consistant consumption patterns, and a longer operational life with minimal material waste. It would also be highly desirable to provide a sacrificial anode device that could be easily mounted directly on essentially any structural surface which is prone to corrosion, and could be easily replaced when necessary.